This invention relates to an aluminum nitride sintered body and a process for producing the same. More particularly, it relates to an aluminum nitride sintered body having high density and high thermal conductivity, and to a process capable of producing the same at low temperature.
Aluminum nitride (AlN) has high strength at temperatures from room temperature to higher temperatures and is also excellent in chemical durability. Therefore, while it has been utilized as heat-resistant materials, application of aluminum nitride for heat dissipating plate material through utilization of its high thermal conductivity and high electrical insulation is expected to be promising. Such AlN has generally no melting point but will be decomposed at a high temperature of 2789 K. or higher and it is used as a sintered body except for cases where it is used as thin films or the like.
Such an aluminum sintered body is generally obtained by molding and sintering AlN powder. However, when AlN powder alone is used, it cannot be sintered well and therefore it is difficult to obtain a high density sintered body when sintering is conducted by a method other than the hot press method.
Accordingly, when sintered under atmospheric conditions, with an aim to promote the densification of the sintered body, it is generally practiced to add a rare earth element oxide or an alkaline earth metal oxide as the sintering aid to AlN powder. See "Effects of various kinds of additives on sintering of aluminum nitride:, K. Komeya, H. Inoue and A. Tsuge, Yogyo-Kyokai-shi 89 (6) 1981.
By addition of such a sintering aid, the density of the sintered body has indeed considerably been enhanced. However, on the other hand, thermal conductivity of such a sintered body, due to presence of oxygen and other impurities and grain boundaries, remains lower than expected under the pressure situation. More specifically, while the theoretical thermal conductivity is 320 W/m.multidot.k, that of an AlN sintered body is in the range of 20 to 60 W/m.multidot.k.
Further, the temperature at which ordinary AlN powder is sintered is usually very high as 1800.degree. C. or higher, which has been a bar to reduction in cost for production of AlN sintered body.